We are attempting to demonstrate that glycine is utilized as a neurochemical messenger by the identified neurons R3-R14 in he parietovisceral ganglion of the marine gastropod Aplysia californica. These neurons have been shown to contain high concentrations of glycine and a specific glycine uptake system in their cell bodies, and to specifically transport glycine into their axons. All of these observations are consistent with, but not compelling evidence for a neurotransmitter function for glycine in R3-R14. Currently the association of glycine with the characteristic vesicles in R3-R14 and the morphology of the terminals of the branchial nerve axons of those neurons is being investigated. Future investigations will attempt to show that glycine is released in conjunction with electrical activity in R3-R14, to locate the target tissues of R3-R14, and to characterize the biosynthesis of glycine in R3-R14.